Bob Doyle, Columnist
The human body is an amazingly complex and delicate life form. Some of us become very aware of certain parts when we have pain or display abnormal symptoms.
For an overall view, I recommend “The Wonders Inside THE HUMAN BODY,” a Silver Dolphin book, published in 2009. I previously reviewed another Silver Dolphin book, “The Wonders Inside THE EARTH” and found it to be a very fascinating account of our home planet. “The Human Body” has ISBN-13: 978-1-57145-718-9. The author is Jan Stradling with Dr. Robin Arnold as the consultant. “Human Body” has a number of transparent overlays so you can peel away the skin and see the structures underneath.
Here are some important numbers “The Human Body” lists in the first section. Adults have 26 billion brain cells, 650 muscles, 206 bones and 100,000 miles of blood vessels.
The 70 percent water making up your body is in your blood and within your cells. There are 200 different kinds of cells. Your body contains 100 trillion cells, of which 10 percent are human cells. The remaining 90 percent of your cells are bacteria living on your skin, in your mouth and in your intestines.
The human cells are constantly wearing out so each second about 10 million human cells die, being replaced by asexual reproduction. (Just as you never meet the same water molecules while standing in a moving stream, you never meet the same human, even your close friends and relatives!) Your skull is made of 29 bones that enclose your brain and provide the framework on which your face and neck muscles are attached. There are four kinds of human tissue.
Epithelial tissues make up your skin and cover organs. Connective tissues keep organs in place. Muscle tissues allow you to move. Nervous tissues allow communication between the brain and the rest of your body.
Your skin is the largest organ in your body, weighing about 11 pounds for an average adult and covering an area of nearly 22 square feet. The epidermis is the outer layer of the skin and is several cells thick. The dermis is a deeper layer containing tiny blood vessels called capillaries. These capillaries can discharge heat to cool you down or trap heat on cold days.
Hair, skin and your nails are all made of keratin. Some kind of hair covers most of your body save your palms, your feet soles and your lips. The outer layers of your nails, hair and skin is made up of dead tissue. But just under the outer surfaces are new cells, waiting to replace the dead cells that fall off.
As to the brain, the outer layer is the cerebral cortex whose tens of millions of cells communicate your present awareness.
The brain’s medulla oblongata controls your automatic functions such as breathing and digestion. The cerebellum helps maintain your balance and keeps your muscle motion smooth. Some small organs deep inside your brain allow you to experience emotions.
The thalamus manages the flow of sensory information. The hippocampus is essential to remembering and learning. The hypothalamus tells our bodies how to react to different emotions. The amygdala sends a signal to your body when you are fearful or anxious.
The HUMAN BODY’s overlays allow you to see your heart both from the back and the front. The heart contracts and relaxes about 100,000 times a day. It is by far the hardest working muscle in your body, “never going on vacation” or saying, “I’m just too tired to contract, I want to take a nap.” Babies have no fingerprints at birth. The embryo is called a fetus at 8 weeks (after conception). A typical fetus is 5 inches long at 12 weeks. At 38 weeks, the fetus turns itself upside down, in preparation for its passage through the birth canal.
Your biggest bone is the thighbone or femur, which is one-quarter of your height, no matter what your age.
The average person walks 79,500 miles during his lifetime, more than three times the circumference of the Earth.
The image of the outside world is upside down on your retina in the rear of your eye. On the retina, the rods sense light and the cones detect color and detail. The sclera is the white of the eye, the iris is the colored part of the eye and the pupil is the dark dot in the middle of the eye where light penetrates onto the retina. (To be continued next week.)
SKY SIGHTS NOW AND THROUGH NEXT SUNDAY: In the evening, the bright planet Jupiter is prominent in the west; Jupiter is at a 60 degree angle to the sun, being visible all through the evening hours.
In the southern evening sky, the orange planet Mars is about half as bright as Jupiter. Both planets shine steadily, not twinkling as the night stars.
Saturn appears as a bright point among the stars of Libra. Look for Saturn late in the evening in the southeast when it is high enough to observe its rings through a modest telescope.
A narrow crescent moon appears near the planet Jupiter on the evening of May 3. On May 6, the evening moon will appear half full, the best phase for spotting the moon’s craters with binoculars or a telescope. In the eastern morning dawn, Venus is a brilliant point of light.
Bob Doyle invites any readers comments and questions. E-mail him at firstname.lastname@example.org. He is available as a speaker on his column topics.